If we "reject" the doctors' assumption that Mrs. Mallard dies of "joy," from having seen her supposedly dead husband again, what really kills Mrs. Mallard?
In the conclusion of Kate Chopin's short story, The Story of an Hour, Mrs. Mallard, supposedly, died "of joy that kills." While some may accept this as true. Others could easily argue that she did not die of any "joy."
Given that readers see how Mrs. Mallard truly feels about her husband, and his oppressive nature, readers know that she did not die of "joy" at seeing her husband again.
Instead, some readers would tend to lean towards a very different explanation regarding Mrs. Mallard's death. It was most likely shock, and a subsequent heart attack, which killed Mrs. Mallard. This "diagnosis" is made even more believable when Mrs. Mallard's heart condition is mentioned in the opening sentence.
Once Mrs. Mallard got over the initial "shock" of her husband's death, she found a new light inside herself (brought on with the help of the new life blooming outside). She was excited that she would never again be oppressed and controlled by Mr. Mallard. Even exiting her bedroom, Mrs. Mallard was a different woman descending the stairs like "a goddess of Victory." When Mrs. Mallard comes to see the door open, and her husband walk in, her heart simply gave up. It (her heart) could not take returning to the relationship she had within her marriage.